With Kalkhoff's new Impulse crank drive and Shimano's latest 11-speed hub gear, is this latest £2495 incarnation of the Agattu the best yet? Read the review in full.

Posted by Peter Eland on Thursday 6 Sep 2012

This review appeared in Electric Bike magazine Issue 5. You can download it as a high resolution PDF. Or click the viewer below to read the review with the original print layout - or scroll down for the full text and images online!

Review: Kalkhoff Agattu C11 Impulse Premium

With Kalkhoff's new Impulse crank drive and Shimano's latest 11-speed hub gear, is this latest £2495 incarnation of the Agattu the best yet?

German brand Kalkhoff have had an Agattu in their e-bike line-up for several years; until 2012 they were powered by Panasonic crank drive motors with, as technology developed, ever increasing battery capacity. This year, though, Kalkhoff launched their own 'Impulse' drive system, with the aim of addressing some of the perceived shortcomings of the Panasonic: its lack of a speed sensor (so it has to cut out at a particular pedalling rate, equivalent to 15.5 mph in top gear), its power profile (designed for stricter Japanese regulations) and its lack of flexibility (no re-programming possible). The new Impulse drive addresses all of these, and adds on-bike charging (the Panasonic battery had to be removed for charging), the option of an informative handlebar display, and (especially for mainland Europe) the ability to be combined with a coaster (back pedal) brake. It also adds a 'push assist' function for low-speed assistance without pedalling.

Our bike, supplied by Kalkhoff's UK importers 50cycles, is the top of the range Impulse model, complete with 11-speed Shimano hub gear, the large display and full 540 Wh battery (36V, 15 Ah), promising a range of "up to 120 km/75 miles". Three frame sizes are available across diamond frame and step-through versions: ours was a medium with cross-bar.

Some of the first Impulse bikes were supplied with an earlier version of the control software: ours came pre-installed with the latest update giving, they say, improved hill-climbing performance. If further software updates are needed and no dealer is nearby, importers 50cycles can post out a small device for customers to do the update at home.

A battery life of 1100 charging cycles is claimed for the 540 Wh battery, suggesting a life of over three years in everyday use, although the warranty period for both bike and battery is two years.

50cycles have two bases themselves (in Loughborough and London) but there is also a network of six further dealers selling Kalkhoff bikes, plus around 70 'owner demonstrators' around the country who are willing to offer potential buyers test rides (not necessarily of this model, of course).

Contact 50cycles or see their website for all of the details.

» ON THE BIKE

The C11 is equipped with a fairly high end set of cycle components on its alloy frame. The Shimano 11-speed hub gear is their newest model, promising a wider gear range than the commoner 8-speed version, but still with the low maintenance of fully enclosed gears. It's controlled by a 'trigger' type shifter, with separate levers for up and down shifting, nicely placed below the bars so you don't have to release your grip to change gear.

The brakes are one of my favourite systems, Magura hydraulic rim brakes. I use these on several of my own bikes and they've proved truly low-maintenance over several years, retaining a silky smooth feel long after even the best cable brakes would be starting to stick. Replacing brake blocks is very easy too - just snap the old ones out and the new ones in. Thumbs up from me.

Everything else is good too, so I won't spend too long detailing the rest of the parts. On instead to the Impulse system! It nestles neatly between seatpost and rear mudguard, with a curve to the battery pack to maximise its use of space. The motor itself is built in around the bottom bracket, and it all sits within the 'visual envelope' of the plastic chainguard.

The large battery pack curves around the rear wheel (with a mudguard in between to keep it clean).

The battery removal system is very similar to the Panasonic's: once unlocked it just swivels out, and replacement simply involves seating the base and clicking the top back in. It's fast and easy, and cleverly the battery keys (two provided) also fit the frame lock. This puts a steel bar between the spokes of the rear wheel to immobilise the bike, a good way to prevent opportunistic theft (but no substitute for locking it to something substantial).

The Magura HS33 hydraulic brakes are smooth and powerful. Note also the AXA frame lock, which uses the same keys as the battery.

From the motor unit a short wire runs to the wheel rotation sensor, which detects a magnet attached to a spoke on the rear wheel. The rest of the wiring runs up inside the frame to the headset area before emerging to run to the handlebar units.

The speed sensor detects the passing of a magnet attached to one of the spokes on the rear wheel.

Right next to your hand is the control console, with the on-off button and power level up and down switches (three levels plus 'off'). The 'set' button between them scrolls through the display modes on the LCD display at the centre of the handlebars, and if you hold it down for a few second it brings up a menu system offering options including language choice, units, wheel circumference settings and many more.

The control buttons are in easy reach of your left hand, as is the bell.

The 'lump' you'll see just below the console is a bell, very conveniently sited, and nestling behind that is the button for push assist - an aid to walking with the bike, helping you push it up ramps, for example. The bell does get in the way of using it a bit, but it's a function I rarely felt the need for.

A separate hub dynamo in the front wheel powers the lights, which are top quality LED units front and rear. A switch on the front light controls them, or just set it to 'sensor' mode and they'll operate automatically.

Finally, the bikes comes with a two part charger, so that you can top up the battery either on the bike or away from it (if you have no power point where you park the bike). The charger looks rather like a black version of a Mac Mini computer for some reason, and it should charge from empty in around three hours: quite fast for such a large battery. To charge away from the bike, the charger cable plugs into a 'dock' onto which you can place the battery, just as you would have done for the previous Panasonic system.

» ON THE ROAD

Even with just a medium frame and with the stem set at a fairly moderate angle, the swept-back bars give a fairly sedate, upright riding position. This takes the weight off your wrists and eases the bend of your back, at the cost perhaps of rather more resistance into a headwind. A cycle dealer would have no problem making a few alterations if you want something more sporty.

It was also good to find that the C11's suspension seatpost worked well, moving responsively as the rear wheel hit bumps. The front suspension too responded well. It has a lockout function but I didn't feel much need to use it even on longish hills.

The brakes were superb, among the smoothest and most powerful I've tried. Perhaps the smoothness was down to brand new rims and brake blocks, but still impressive. The levers have a lovely feel and not much pressure is required for stopping.

Overall, the bike aspects were really good, with a stable, rattle-free ride and components which really operated well.

I'll touch on the gears in a moment.

With the electrics turned on, the LED display comes to life (it remembers the power setting you were using when you last switched it off) and you're ready to set off.

It did surprise me that the power assist didn't start immediately when you start pedalling, as it does with most crank motors. Instead, it seems to ramp over a half rotation or so. Kalkhoff say that this 'soft start' system makes setting off more predictable, with no chance of 'pedal kick' if you rest a foot on the pedals while stationary. True, but I did miss the instant power assist when setting off - that first pedal stroke is exactly when you need full assist most, especially on hill starts.

After that, though, the power assist works in true torque sensor fashion: the harder you pedal the more it assists. And it does this very well, without any uneven pulsing, and however fast you choose to spin the pedals. As your pedalling speed rises so does the noise level - if you move your feet only gently, it's very low and quiet, rising to a more urgent buzz if you really spin them round.

Setting off from lights, this freedom to pedal as fast as you like is very welcome: it frees you from needing to shift up gears for those first few yards.

That's particularly useful on this model, as there's an interplay between the drive system and hub gear here which has both positive and negative consequences. The Shimano 11-speed hub shifts really well, and it's even easy to click through several gears at a time, whether you're at a standstill or moving.

But what it won't do is shift while under load: it lets you change gear at the handlebars, but then the mechanism within the gear won't actually implement the shift until the load going through the transmission drops to a 'safe' (for the gear internals) level. This should work really well to prolong the life of the hub gear, but it does mean that it's very hard to shift (especially into higher gears) without easing off on the pedals to make the change happen. And that easing off also leads to the power assist cutting out, then ramping up again before it kicks in again at full power. So as you're going up through the gears, power assistance is 'punctuated' each time by the gear change. It's not a problem at all once you're used to it, just a quirk you quickly adapt to.

As you speed up, the tail off as it comes to the legal cut-off speed of 25 km/h (15.5 mph) is very gentle indeed - in fact it's often still giving a tiny bit of power (according to the display) as you go through 17 mph. You'll need to be in one of the higher assist modes to get there - in 'eco' it tails off around 14 mph, and feels noticeably less eager.

Up hills the power level feels good, and with just moderate effort in your pedalling it will take you up even the steepest hills, as long as you've selected a reasonably suitable gear. One of the display modes is of instantaneous power assist level, and it's interesting to see this reach four or more bars out of its five as the power assist works harder to help you up. Other display modes include trip and total distances, average speeds, and one purporting to show how much CO2 emission you've saved compared to travel by car.

More usefully, your road speed is always displayed, as is battery status and an estimate of the range remaining.

The display console is large and clear. It’s mounted solidly at the centre of the handlebars.

On our demo bike this started at 48 miles with a full charge, and this reduced pretty much in line with my actual mileage over the following days. I think it's always calculated on the basis of the assist being in 'power' mode (its highest setting) as selecting the presumably more economical 'sport' or 'eco' modes didn't affect the figure.

Strangely, though, with around 14 miles to go the range remaining figure plummeted suddenly to two - but it continued to work for around another ten anyway. I couldn't find details of how the figure is calculated, but it must always be an estimate at best. And it's good that it was under, rather than over estimating.

If you're relatively economical in your riding the claimed 75 miles range on a charge should be achievable, barring major hills. The bike rides well enough without the assist, although the weight is noticeable. Certainly it's no great sacrifice to switch off the assist on the flat and downhills if you're trying to save power.

Quality forks and LED lights.

» SUMMARY

The Agattu C11 is a strong showcase for the new Impulse drive, and the bicycle aspects all perform well. In almost every riding situation the electric assist is also excellent, with plenty of power to add to your own pedalling, and an excellent display.

My only niggles are the non-instant start of the assist as you set off, and the somewhat erratic range readout, although in fairness it's probably near impossible to make any such figure truly accurate. I suppose I should also count as a niggle that it's not silent, although it's very much at the same modest noise level of other crank drives.

Overall though, a highly impressive machine with substantial range, a strong company behind it and with the mechanical aspects a pleasure to use. You're paying for this quality, admittedly, with the £2495 purchase price, but if that budget's in your ballpark I'd recommend trying it out and making your own judgement as to the value: an expensive bike you really enjoy using will always be a better buy in my book than a bargain which reminds you of its cheapness on every ride.Peter Eland

Available from:

Just a clarification on the "soft start" reported here. One of the many advantages of the Impulse system is the ability to change performance profiles, this particular model was set up for hill-climbing.

Kalkhoff's latest software provides for a boost as start-up if preferred.

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